Vacuum Brazing of Ce:LuAG/Al2O3 Composite Ceramic Phosphors for Improved Light Output Performance

Ce:LuAG ceramic phosphors are promising green phosphor conversion materials for high-brightness lighting and display. However, despite its excellent resistance to thermal quenching, Ce:LuAG still suffers from thermal drop of the luminescence under high-power excitation, particularly under ultra-high-brightness laser excitations. This work investigated the effects of excessive Al 2 O 3 addition to the Ce:LuAG ceramic phosphor combined with vacuum brazing on the luminescence thermal stability. Experimental results indicate that 10 wt.% Al 2 O 3 addition improves the Ce:LuAG ceramics microstructure, thermal conductivity, and in result enhances the comprehensive luminescence performance. Cross-sectional BSE and EDS analysis reveals a dense, crack-free brazed interface with Ti enrichment at the ceramic/braze boundary, confirming the formation of a Ti-O reaction layer that enables chemical bonding and efficient heat dissipation. The sample with an additional 10 wt.% Al 2 O 3 brazed at 870°C achieves light conversion efficiency of 253 lm·W −1 at an excitation light power of 2 W, with light conversion efficiency drop of only 10% at a light power of 8 W. (For the samples without additional 10 wt.% Al 2 O 3 , the light conversion efficiency drop exceeds 15.5% at an excitation light power of 8 W.) With light output exhibiting good linear correlation with excitation blue laser power across the 0–30 W range ( R 2 = 0.99784). The illuminance of the ceramic increased linearly within the 10–80 W range, the brazed sample at 870°C reached 2.05 × 10 4 lx under a light excitation power of 90 W, exhibiting better luminescence thermal stability than the Ce:LuAG ceramic phosphors without excessive Al 2 O 3 addition. The combination of excessive Al 2 O 3 addition and vacuum brazing is an effective solution for achieving robust luminescence from Ce:LuAG ceramic phosphors toward high-power laser excitations.